Femtocell base stations in a Long Term Evolution (LTE) communication network (otherwise known as Home evolved Node Bs—HeNBs—or Enterprise evolved Node Bs—EeNBs) are small, low-power, indoor cellular base stations for residential or business use. They provide better network coverage and capacity than that available in such environments from the overlying macrocellular LTE network. In addition, femtocell base stations use a broadband connection to receive data from and send data back to the operator's network (known as “backhaul”).
As femtocell base stations can make use of the same frequencies as macrocell base stations in the macrocellular network, and as they are located within the coverage area of one or more macrocell base stations in the macrocellular network, it is necessary to ensure that downlink transmissions from the femtocell base station to mobile devices (otherwise known as User Equipments—UEs) using the femtocell base station do not interfere substantially with downlink transmissions from macrocell base stations to mobile devices using the macrocell base stations.
Typically, this interference is mitigated by placing a cap on the power that the femtocell base station can use to transmit signals to mobile devices. The cap on the power can be set such that, at a specified pathloss from the femtocell base station (for example 80 dB), a signal received by a mobile device from a macrocell base station would meet a specified quality level (for example a target signal to interference plus noise ratio—SINR). The determination of the cap is subject to a minimum and maximum power restriction on the transmission power of the femtocell base station, for example 0.001 W and 0.1 W respectively.
However, this approach has limitations in that the transmission power of the femtocell base station will be capped regardless of whether there are any mobile devices near to the femtocell base station that are communicating with a macrocell base station and that need protecting. This cap can lead to the data throughput for mobile devices communicating with the femtocell base station being unnecessarily restricted.
Therefore, there is a need for an improved approach for setting the maximum permitted transmission power for downlink transmissions from base stations.